Image-forming process utilizing contact electrification

ABSTRACT

ELECTROSTATIC CHARGE IMAGES ARE PRODUCED ON A MEMBER HAVING AN ELECTRICALLY INSULATING SURFACE WHEN IT IS INTIMATELY CONTACTED WITH A PORTION OF A SECOND MEMBER INCLUDING ORIGINALS TO BE COPIED THAT IS, AT LEAST IN PART, TRIBOELECTRICALLY SEPARATED OR REMOTE FROM THE INSULATING SURFACE. AFTER THE SECOND MEMBER AND INSULATOR ARE SEPARATED, A LATENT ELECTROSTATIC CHARGE IMAGE IS PRESENT UPON THE ELECTRICALLY INSULATING SURFACE IN A PATTERN CORRESPONDING TO THE TRIBOELECTRICALLY SEPARATED OR REMOTE AREAS OF THE ORIGINAL THAT ARE INTIMATELY CONTACTED WITH THE INSULATING MEMBER. THIS LATENT IMAGE CAN BE RENDERED VISIBLE BY ELECTROSTATIC DEVELOPMENT TECHNIQUES. ALTERNATIVELY, A SECOND MEMBER THAT IS UNIFORMLY TRIBOELECTRICALLY SEPARATED CAN BE INTIMATELY CONTACTED WITH AN ELECTRICALLY INSULATING MEMBER OR SURFACE IN AN IMAGEWISE FASHION, THEREBY PRODUCING A LATENT ELECTROSTATIC CHARGE IMAGE ON SUCH INSULATOR IN A PATTERN CORRESPONDING TO THE IMAGEWISE CONTACT. THIS IMAGE CAN ALSO BE MADE VISIBLE BY ELECTROSTATIC DEVELOPMENT.

nitecl States Paten Int. Cl. G03g 13/22 US. Cl. 96-1 10 Claims ABSTRACT OF THE DISCLOSURE Electrostatic charge images are produced on a member having an electrically insulating surface when it is intimately contacted with a portion of a second member including originals to be copied that is, at least in part, triboelectrically separated or remote from the insulating surface. After the second member and insulator are separated, a latent electrostatic charge image is present upon the electrically insulating surface in a pattern corresponding to the triboelectrically separated or remote areas of the original that are intimately contacted with the insulating member. This latent image can be rendered visible by electrostatic development techniques. Alternatively, a second member that is uniformly triboelectrically separated can be intimately contacted with an electrically insulating member or surface in an imagewise fashion, thereby producing a latent electrostatic charge image on such insulator in a pattern corresponding to the imagewise contact. This image can also be made visible by electrostatic development.

This invention relates to the production of images and particularly to the production of triboelectric, electrostatic charge images and visible images corresponding to the electrostatic charge images.

The production of electrostatic charge images is known. Typically, such images are produced by methods of electrophotography, wherein a photoconductive electrically insulating layer is first uniformly electrically charged, then imagewise exposed to light or other activating electromagnetic radiation which selectively dissipates the charge in illuminated areas, leaving an unexposed imagewise latent electrostatic charge image on thephotoconductive layer. This latent electrostatic image can be made visible by depositing triboelectrically charged toner particles according to well-known techniques of powder or liquid electrophotographic development.

Alternatively, the susceptibility of a surface to charging can be modified, such as is disclosed in British Pat. 1,085} 5 7 3, whereupon uniform treatment with a charging means produces a varying charge image due to the differential chargeability of such surface. Such a method obviates the necessity for an exposure means. Rendering the electrostatic image visible can also be accomplished by known electrophotographic development means.

Known methods of producing electrostatic charge images, however, require an over-all charging step which necessitates the use of inconvenient charging and related apparatus. Then too, exposure or alternative physical treatments are required to secure an imagewise charge formation.

Accordingly, it is an object of this invention to provide a new process for preparing electrostatic charge images.

Another object of the present invention is to provide a novel process for preparing electrostatic charge images without need for either a separate overall charging means,

light exposue or preliminary modification of the ultimately charged surface.

3,579,330 Patented May 18, 1971 Still another object of the present invention is to provide a new process for preparing visible images by electrostatic means.

Other objects and advantages will become apparent from a reading of the following specification and appended claims.

The objects of the invention described herein are accomplished by an image-forming process that includes:

(a) Intimately contacting an electrically insulating member having a surface resistivity of at least about 10 ohms per square with a portion of a second member whose contacting portion is, at least in part, triboelectrically separated from the electrically insulating member,

(b) Separating the electrically insulating member and the second member and forming a latent electrostatic charge image on the electrically insulating member in a pattern corresponding to the areas of contact with triboelectrically separated portions of the second member, and

(c) Contacting the electrically insulating member with an electrostatic developer composition containing a toner, whereupon an imagewise distribution of toner is produced on the electrically insulating member in a pattern corresponding to the latent electrostatic charge image and thereby rendering the latent image visible.

Electrically insulating members that are advantageous in the practice of the invention described herein include insulating members having a surface resistivity in excess of about 10 ohms per square as measured by Van der Pauw technique, described in Phillips Research Report, 13, 1-9 (1958). Preferred insulating members or insulators exhibit a surface resistivity of at least about 10 ohms per square.

Generally, any insulator having the described surface resistivity is suitable, but particularly preferred insulating members are those having extremely smooth surface and formed from resins such as hydrophobic polymers conventionally employed as photographic film support material. The presence of a smooth surface promotes intimate contact between original and insulator. Exemplary of advantageous polymeric materials are such hydrophobic compositions as esterified cellulose derivatives like cellulose triacetate and cellulose acetate butyrate, as well as other polymers including poly-a-olefins such as polystyrene, polyethylene and polypropylene, and polyesters such as poly (ethylene terephthalate) etc. A wide variety of the other well-known film-forming, hydrophobic homopolymers or copolymers which have suitable surface resistivity as described hereinabove can be used as the insulating member.

The insulating member is intimately contacted with a second member that can be an original to be copied, and the two are then separated, leaving an imagewise electrostatic charge image on the insulator. The mechanism of the subject invention is thought to involve the transfer of electrons from either second member to insulator or in the opposite direction and has been designated contact electrification or static electrification. The theoretical aspects of this invention are described with considerable detail in Hersh and Montgomery Static Electrification of Filaments, Theoretical Aspects, Textile Research Journal, XXVI, December 1956, p. 903.

More particularly, the insulating member and at least part of the second member are separated from each other in the triboelectric series, an artificial framework that positions substances according to their electrochemical potentials. Determining the triboelectric series position of a material is accomplished merely by contacting two materials, separating them and detecting the charge p0- larrty of each with an electrometer or other suitable charge recording instrument. The series is then conventronally complied in descending order from positive to negative such that a material higher in the series charges 3 positively with respect to those lower in the series. Although any member of the triboelectric series is itself electrically neutral, when two members (their surfaces differing in electrochemical potential) are placed in intimate contact, an imbalance in surface potential is created at their contact interface and electrons will tend to flow from the member having a higher energy level to the member having a lower energy level, thereby seeking to equalize the noted surface potential imbalance. When the members are separated or removed from intimate contact, the charge transfer that has occurred between such members to equalize their varying surface potentials is not given sufiicient time to reverse itself and thereby reattain the original electrical neutrality of each member. The net effect is an electrical surface charge present on each member, the charges being of equal magnitude but of opposite polarity. The member that is higher in the triboelectric series will have a positive polarity charge.

The present invention is concerned with members that are separated or remote from each other in the triboelectric series. That designation of separation or remoteness, as it is used herein, indicates a triboelectric series disparity between such members in the ultimate image area that is sutficient to produce a latent triboelectric charge image on the subject insulating members which is of a magnitude susceptible of intensification to a visible image by known methods of electrostatic development. Where certain of the subject second member originals have a differential triboelectric separation from the in.- sulating member, part or all of the triboelectric charge formed as noted herein can be suflicient to promote visible image development by electrostatic techniques. Typically, members separated in the triboelectric series are those which are contact electrified or triboelectrically charged, either positive or negatively, to at least about 50 electrostatic units/cm. in those areas intended for image development.

Where an original has a surface which exhibits more than one electrochemical potential, as on an ordinary printed sheet containing inked or pigmented images for example, each of which surface potentials is, in the triboelectric series, separated from that of the electrically insulating member but in an unequal degree, then the charge transfer between members in each area will be only so much as is necessary to achieve equilibrium of surface potential at each contact interface. As such, greater triboelectric separation or remoteness between contacting surfaces promotes a higher degree of charge transfer than does a lesser separation.

Separation of the intimately contacted members promotes charge transfer in the opposite direction, thereby tending to re-establish the original charge neutrality of each member. However, when one member is an electrical insulator, such as those described herein, the rate of charge transfer is restrained due to the high surface resistivity at the contact interface. A charge pattern remains on each member when the members are separated with at least moderate speed, such charge patterns corresponding to the contact area between surfaces that are separated or remote in the triboelectric series. Due to the resistance of the insulating member, the charge pattern or image present thereon is retained for substantial periods of time and is subject to intensification to a visible image by conventional electrostatic dry and liquid development techniques.

Advantageous second members include those that are originals to be copied having a surface with an image area and a non-image area that, in the triboelectric series, are separated or remote from each other and differentially positioned with respect to the electrically insulating member, with at least one of the image and nonimage areas also being triboelectrically separated or remote from the electrically insulating member. These originals can be duplicated in accordance with the present process by being placed in intimate contact with an in sulating member as described herein. Such originals typically comprise a support having coated thereon an imagewise distribution of a material that, in the triboelectric series, is differentially remote from the electrically insulating member than is the support. Advantageous supports are widely variable and include such materials as metals, photographic film base materials, polymers, cellulose esters, and paper including paper coated with poly-a-olefins such as polyethylene and polypropylene, as well as numerous other well-known materials that are used in the printing and other reproductions arts. Additionally, materials not normally utilized in such fashion can be advantageous supports herein if the requisite triboelectric separation is obtained. In a like manner, the material that is coated on the support can be extensively varied and need only modify the triboelectric characteristics of the support in order to obtain the triboelectric separation desirable herein. As such, the coated material'can be visible or invisible and can be such items as resins, inks, pigment dispersions, dyes, metallic coatings and the like.

Exemplary of specific advantageous originals are such items as electrostatic photocopies containing toned images of dyed or pigmented resins, ink printed copy such as books and newsprint, paper stock bearing characters of such materials as ball-point pen, india ink, graphite dispersions and pencil lead, thin layer photographic negatives and transparencies like microfilm containing sil ver images, and numerous other originals wherein the triboelectrically remote image area and non-image area are unequally separated, in the triboelectric series, from the insulating member. Where photographic negatives and other photographic elements having a silver image in gelatin are employed as originals, contact electrification occurs in areas corresponding to nonimage areas of the original.

The image and non-image areas of such an original need only exhibit such an unequal separation from the triboelectric series position of the insulator as will promote its advantageous imagewise charging; both areas can be above the insulator, both areas can be below the insulator, one area can be equal to the insulator and one either above or below the insulator, or one can be above and one below the insulator in order to secure a latent electrostatic charge imageof adequate strength for subsequent electrostatic development to a visible image. If both image and non-image areas of the original are either above or below the triboelectric series position of the insulator, it is" preferred that the portion to be reproduced is most remote.

Certain electrostatic developer compositions include a positively charged toner that is attracted to negative electrostatic images, whereas other toners are charged negatively and attracted to positive images. In the practice of the present invention, when an original has an image area and a non-image area which, in the triboelectric series are remote from each other and respectively positioned above and below the insulating member, a visible image can be formed. in either area by the use of a developer having the properly charged toner since the insulator is charged positively by contact with materials which are positioned below it in the triboelectric series, and negatively by contact with materials that in the series are above the insulating member.

Other advantageous second members that are originals to be copied include those having a raised image or image area that, in the triboelectric series, is desirably separated from the electrically insulating member and forms a latent electrostatic charge image thereon in accordance with the subject process. This type of original includes such members as relief printing plates having, for example, a relatively thick, imagewise distribution of polymer on a support, as well as additional etched and other such surfaces that have an image area that is raised above the non-image or background area. The production of visible images is again accomplished by electrostatic development means, wherein only positive images are produced,

since the portion of the insulator corresponding to the background or non-contact areas of the original remains electrically neutral and thereby not amenable to electrostatic development.

In carrying out the present electrostatic image-forming process, contacting the electrically insulating member and the second member which can be an original to be copied is advantageously in intimate fashion. It is to be emphasized that during the contact period, the two members remain stationary with respect to each other, there being no frictional contact by rubbing to produce an overall charge image. This is desirable in each instance, regardless of variations in the character of contacting members. Conventional triboelectric charging by rubbing would not permit the imagewise charge transfer which is integral to the present invention.

Overall intimate contact is normally accomplished by first positioning the insulator and second member in face to face contact, after which they are pressed together by an outside source, typically a roller apparatus or a flat press. A single hand or power roller can be used, the original and insulator being maintained on a flat surface, or one can employ dual rollers wherein the sandwich of original and insulator are passed between two rollers rotating at such speeds as maintain the same linear rate between rollers at their outer curved surfaces. Conventionally forces of up to about 150 p.s.i. are suitably applied to the roller or rollers and promote desirable images. Greater force can be used, if desired, but should not normally be required. When originals bearing a raised image area are pressed against an insulator such as herein described, more moderate forces are typically employed, and generally in the range of from about to about 50 p.s.i. Forces considerably in excess of about 50 p.s.i. applied to a fiat press or rollers tend to compress and deform the originals raised image, and thereby promote distortion in the electrostatic image formed on the insulator. In certain cases, the raised image can be flattened, as with gelatin layers on certain relief plates or thick-layer photographic transparencies, causing unwanted charging in areas corresponding to non-image background region. Where particularly rigid and dimensionally stable originals are used, however, contact force can be suitably increased. After being pressed together, original and insulator are then somewhat rapidly separated, while still maintaining the stationary relationship between members, whereupon an imagewise electrostatic charge is present upon the insulating member.

As previously noted, upon separation of the two members subsequent to overall intimate contact, charge transfer tends to occur in the opposite direction. Such activity can be accompanied by sparking or charge breakdown at the contact interface as original and insulator are separated. Such spark discharge causes non-uniform charging and deleteriously affects the insulators electrostatic image present after separation. Accordingly, where such charge breakdown tends to occur, it is preferred that, during separation, the back surface of each of the original and the insulating member is contacted to an electrical conductor and that the two conductors are connected by an electrical conducting path during separation. Such measures provide an alternate route for partial charge equalization and tend to eliminate sparking at the contact interface between original and insulator. Suitable conductors include such items as metal foil and metal plates and, especially as regards the insulator, can be a vacuum-deposited nickel, aluminum or additional conducting metal or other layer applied to the reverse side of the member. Any of the conducting layers utilized in electrophotographic elements can be used including such non-metallic conducting layers as cuprous iodide.

Alternatively, an insulating member of this invention can be positioned against a second member that has a surface that, in the triboelectric series, is uniformly separated from the electrically insulating member. The members are then intimately contacted in imagewise fashion and separated, whereupon a latent electrostatic charge image such as those described hereinabove is present on the electrically insulating member in a pattern corresponding to the imagewise intimate contact. This latent image can then be intensified to a visible image by well-known electrostatic development techniques.

Additionally, pressure deformable members that are a composite fabrication, having an upper, electrically insulating surface and a lower surface that is uniformly separated from the insulating surface in the triboelectric series, can be superposed to form a stack of such members in which an upper surface and a lower surface are contiguous at each interface between adjacent members. These superposed members can be pressed together in an imagewise fashion, so that the electrically insulating upper surface of each member is brought into imagewise intimate contact with the contiguous lower surface of an adjacent member at their contact interface, and then separating as previously described to form a latent electrostatic charge image on the electrically insulating surface in a pattern corresponding to the imagewise intimate contact with a triboelectrically remote lower surface of an adjacent member. This latent image can then be rendered visible by electrostatic development techniques such as are described elsewhere herein.

Exemplary of such composite members are supports such as the insulating members described hereinabove, that are coated on one side with a material that is triboelectrically separated or remote from such a support. Alternatively, the composite member can be a support such as paper, metal and the like, that is coated on one side with an insulating resin such as those described above in conjunction with the insulating members. In this way the triboelectric disparity between upper and lower surface is obtained. Imagewise intimate contact can be achieved according to numerous techniques. Superposed composite members such as those mentioned herein can be placed in a typewriting apparatus and intimately contacted by pressure from the type. A pencil, ball-point pen, stylus or other like tool can be used to provide imagewise contact pressure. In like fashion, the same results can be obtained when an insulating member is positioned against a triboelectrically remote second member, except that only one copy is obtained. In yet another aspect, an insulating member can be used in a typewriter with a triboelectrically separated or remote material being employed in lieu of the conventional inked ribbon, the striking typewriter keys providing imagewise contact pressure through the triboelectrically remote material superposed on the insulating member. Development of the resulting latent electrostatic charge images by electrostatic means produces YlSlblC images corresponding to the pattern of imagewise intimate contact.

Development of the latent electrostatic charge images prepared as described herein typically comprehends contacting the insulating member with an electrostatic developer composition such as those including a colorant material such as carbon black, a binder material such as a polymeric, thermoplastic resin and a carrier material such as iron filings or glass beads. Mutual rubbing of colorant and binder (which are a composite solid dispersion) against the carrier operate to produce an electrostatic charge on the colorant-binder combination. Upon such contact, an unexposed imagewise pattern of the charged colorant-binder composition adheres to the oppositely charged areas of the insulating member. Subsequent heating of the element causes melting of the thermoplastic binder, permanently fixing the image. In addition to the conventional electrophotographic developers described hereinabove, other advantageous developer compositions include liquid developers such as dyed resin and pigment types having toner particles dispersed in an insulating liquid carrier vehicle and which are conveniently fixed by either fusion or solvent evaporation, as well as other dry developers which incorporate a wide selection of pigments, dyes and thermoplastic resins. Alternatively, in lieu of fixing the permanent image on the insulating member, the imagewise pattern of developer can be transferred, by means such as contact transfer, for example, to another support like paper and fixed thereon by such means as are described hereinabove to prepare a permanent transfer image.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 A piece of single coated, processed industrial X-ray film bearing a visible silver in gelatin photographic image on a poly(ethylene terephthalate) film support is placed on a grounded, polished metal plate with the silver images upward and not in contact with the plate. A piece of 0.004-inch thick poly(ethylene terephthalate) film support material is placed atop the X-ray film and in contact with its silver image surface, the film support surface not in contact with the X-rayed film having a vacuum-deposited aluminum layer coated thereon. The electrical resistance of this aluminum layer is about ohms per square. Intimate contact between the X-ray film and the poly(ethylene terephthalate) is accomplished by rolling with a fairly hard rubber roller, to which a force of about 80 lbs. is applied. After rolling, the conducting aluminum layer on the poly(ethylene terephthalate) film is connected to the grounded metal plate and the two members are stripped apart. A latent electrostatic charge image is present on the poly(ethylene terephthalate) insulating member in those areas corresponding to the non-image areas of the X-ray film original. This latent electrostatic charge image is developed to a visible image by dipping the insulating member into a liquid developer composition containing about 5 ml. of a blue commercial lithographic ink dissolved in about 80 ml. of cyclohexane. Upon solvent evaporation, a stable visible image is present in a pattern corresponding to the electrostatic image.

EXAMPLE 2 Four additional electrostatic charge images are prepared and made visible according to the procedure of Example 1, except that the originals to be copied are silver images in gelatin on processed microfilm, a photolithographic element having an aluminum support carrying an imagewise distribution of a hydrophobic, electrically insulating polymer and a photographic element bearing a conventional high resolution silver image in gelatin respectively. The copies obtained are all of the quality obtained in Example 1. A

EXAMPLE 3 An electrostatic charge image is prepared and made visible according'to the procedure of Example 1, except that the poly(ethylene terephthalate) insulating member has a thickness of 0.002 inch. The copy obtained is commensurate in quality that of Example 1.

EXAMPLE 4 An electrostatic image is prepared according to the method described in Example 1, except that the second member original to be copied is an electrophotographic copy comprising a powder toned and fused image on paper produced by a Model 914 copying machine marketed by the Xerox Corporation. The latent electrostatic charge image is rendered visible by dipping the insulator in an electrostatic developed composition having the form ula 0.1 gram of a mixture of '1 part by weight of phalocyanine green pigment (Solfast Green, Sherwin-Williams Company) and 4 parts of a glyceryl phthalate linseed modified alkyd resin (Dyal XLG-l07, Sherwin-Williams Company) dispersed in 20 m1. of cyclohexane and 80 ml. of 1,1,2-trichloro-1,2,2,-trifiuoroethane. The visible image is similar to that of Example 1.

8 EXAMPLE 5 Six additional electrostatic images are prepared and rendered visible according to the procedure of Example 4, except that the originals to be copied are:

(a) a sheet of bond paper bearing blue color ballpoinnt pen ink writing,

(b) a sheet of bond paper bearing writing from a felt tip ink pen,

(c) a sheet of bond paper bearing writing in india ink (Higgins American India ink marketed by Higgins Ink Company, Inc.),

(d) a sheet of bond paper bearing writing from a No. 2

graphite lead pencil,

(e) a sheet of bond paper bearing writing in a dispersion of colloidal graphite in mineral spirits (Dag Dispersion No. 2404 marketed by Acheson Colloid Company),

(f) a sheet of newspaper,

and except that the insulating members are:

(1) cellulose triacetate in the case of original (0), and (2) polystyrene in the case of original (f).

Images obtained are as those of Example 4, except that the image obtained from original (b) is of a slightly lower quality.

EXAMPLE 6 An electrostatic image is prepared according to the procedure of Example 1, except that the original to be copied is a photographic color positive transparency comprising a cellulose acetate support bearing a dye relief image in gelatin which is placed in contact with the insulator which in this case has a conducting foil positioned over its back surface. Additionally, the rolling pressure is reduced to about 15 p.s.i. After stripping the original and insulator apart, a liquid electrostatic developer like that described in Example 4 is flowed over the insulator bearing an electrostatic image, thereby producing a corresponding visible image.

EXAMPLE 7 Electrostatic images are prepared and rendered visible according to the procedure described in Example 6, except that the color transparency is fastened to a grounded metal roller and the insulator and metal foil are positioned over the original. The metal roller is maintained against a second, rubber roller in such a manner that when the rollers are rotated in opposite directions, the sandwich of original, insulator and conducting metal foil are pressed together while passing between the rollers. Additionally, a known compressive force is applied to the sandwich by hanging weights on a peg fastened to the axle of the rubber roller. Good visible copies are obtained after development with normal forces ranging from 7 to 15 lbs. between the rollers. In several instances the visible images are transferred to a receiver sheet of ordinary bond paper prior to drying.

EXAMPLE 8 A sheet of 10 mil cellulose triacetate film base material is placed over a sheet of 3 mil poly(ethylene terephthalate) polyester film. Information is recorded on the top sheet of acetate film with a pencil. The bottom sheet of polyester film is then removed and immersed in a black colored electrostatic developer which contains positively charged toner particles in an insulating liquid. The toner particles of the developer tone the polyester film in the areas where the pencil had pressed the acetate film and polyester film together during the recording of the information. Measurements of the electrostatic charge produced by the pressure contact between the polyester film and the acetate film show the polyester film becomes charged negatively while the acetate film becomes charged positively. As a result, the positive marking particles are attracted to the areas that are charged negatively on the polyester film by the triboelectric contact electrification.

9 EXAMPLE 9 A conducting paper support is coated with an insulating material comprising poly(vinyl butyral) and titanium dioxide. The thickness of the insulating coating is about microns. Two sheets of this composite paper, having an 5 upper surface and a lower surface that are triboelectrically separated, are placed together with the insulating surface of one in contact with the support of the other. Information is recorded on the insulator-coated surface of the top sheet with a pencil. The pressure used to record the information forces the back of the first sheet into intimate contact with the insulator-coated surface of the second sheet. This pressure contact causes charge transfer between the two surfaces, leaving a negative charge on the insulator surface. This negatively-charged latent image is then developed with the liquid developer used in Example 8.

EXAMPLE '10 Multiple images are made by placing a sandwich of ten sheets of the composite paper used in Example 9 into a typewriter with the insulator-coated surface of each sheet toward the typing heads. After information is typed on the top of the first sheet, the stack is removed and each sheet, except the first, is developed by immersion in the liquid developer used in Example 8. The information which is typed on the first sheet is visible on all the other sheets in the stack. Sharpness of the images is superior to that of images made by conventional methods with carbon paper and onion skin copy paper.

EXAMPLE 11 A positive-charged image was formed by using the EXAMPLE 12 A sheet of aluminum foil paper laminate is placed over a sheet of the composite paper used in Example 9 so that the aluminum side of the laminate and the insulator-coated side of the paper are together. Information is recorded on the paper side of the laminate using a pressure stylus. The two are separated and the composite paper is developed as in Example 8. The resulting negatively charged image is a duplicate of the original pressure recording.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. An image-forming process comprising:

(a) uniformly intimately contacting an electrically insulating member having a surface resistivity of at least about 10 ohms per square with a second member whose contacting portion is, at least in part, triboelectrically separated from said electrically insulating member, said intimate contacting comprising pressing said members together with a force sufficient to promote the formation of an electrostatic charge image,

(b) separating said electrically insulating member and said second member to form a latent electrostatic charge image on said electrically insulating member in a pattern corresponding to the areas of intimate 75 10 contact withtriboelectrically separated portions of said second member, said members having an electrical conductor contiguous to each of their non-contacting back surfaces during the period of separation, the conductors being themselves connected by an electrically conducting path, and

(c) contacting said electrically insulating member with an electrostatic developer composition containing a toner, whereupon an imagewise distribution of toner is produced on said electrically insulating member in a pattern corresponding to said latent electrostatic charge image and thereby rendering said latent image visible.

2. An image-forming process as described in claim 1 wherein said electrically insulating member comprises a polymeric resin.

3. An image-forming process as described in claim 2 wherein the polymeric hydrophobic resin is selected from the group consisting of:

(a) cellulose acetate,

(b) polystyrene,

(c) poly(vinyl butyral),

(d) polyethylene, and

(e) poly(ethylene terephthalate).

4. An image-forming process comprising:

(a) uniformly intimately contacting an electrically insulating member having a surface resistivity of at least about 10 ohms per square with a second member that is an original to be copied, which second member comprises a surface having an image area and a non-image area that, in the triboelectric series, are remote from each other, at least One of said image area and said non-image area being triboelectrically separated from said electrically insulating member, said intimate contacting comprising pressing said members together with a force sutficient to promote the formation of an electrostatic charge image,

(b) separating said electrically insulating member and said second member to form a latent electrostatic charge image on said electrically insulating member in a pattern corresponding to the areas of intimate contact with triboelectrically separated portions of said second member, said members having an electrical conductor contiguous to each of their non-contacting back surfaces during the period of separation, the conductors being themselves connected by an electrically conducting path, and

(c) contacting said electrically insulating member with an electrostatic developer composition containing a toner, whereupon an imagewise distribution of toner is produced on said electrically insulating memher in a pattern corresponding to said latent electrostatic charge image and thereby rendering said latent image visible.

5. An image-forming process as described in claim 4 wherein said second member comprises a support having coated thereon an imagewise distribution of a material that, in the triboelectric series, is separated from said support.

6. An image-forming process as described in claim 5 wherein said imagewise distributed material is selected from the group consisting of metals, inks, resins and gelatin.

7. An image-forming process as described in claim 6 wherein said original is a photographic transparency comprising a polymeric resin support having metallic silver in gelatin imagewise distributed thereon.

8. An image-forming process as described in claim 6 wherein said original is a printed copy comprising a paper support having ink imagewise distributed thereon.

9. An image-forming process as described in claim 6 wherein said original is an electrostatic copy comprising 10. An image-forming process comprising:

(a) superposing a plurality of pressure deformable members, each comprising an upper, electrically insulating surface and a lower surface that is separated from said electrically insulating surface in the triboelectric series, to form a stack of said members in which an upper surface and a lower surface are contiguous at each interface between adjacent members,

(b) uniformly intimately contacting said superposed members in an imagewise fashion by pressing said superposed members together in'imagewise fashion such that the electrically insulating upper surface of each member is brought into imagewise intimate contact with the contiguous lower surface of an adjacent member at their contact interface, said intimate contacting comprising pressing said members together with a force sufiicient to promote the formation of an electrostatic charge image,

() separating said members to form a latent electrostatic charge image on the electrically insulating surface of each member in a pattern corresponding to its imagewise intimate contact with a triboelectrically members having an electrical conductor contiguous to each of their non-contacting back surfaces during the period of separation, the conductors being themselves connected by an electrically conducting path, and

(d) contacting the electrically insulating surface of each member with an electrostatic developer composition containing a toner, whereupon an imagewise distribution of toner is produced on said electrically insulating surfaces in a pattern corresponding to said latent electrostatic charge image and thereby rendering said latent image visible.

References Cited UNITED STATES PATENTS 9/1965 Gold 250-65 GEORGE F. LESMES, Primary Examiner separated lower surface of an adjacent member, said I. C. COOPER, Assistant Examiner U.S. Cl. X.R. 

